Radio direction finder



Hh nlimmll J. B. HEFFNER, JR

RADIO DIRECTION FINDER Filed Feb. 28. 1951 v INVENTOR Jari/H #Fmi/e; Je

ATTORNEY April 14, 1953 Patented Apr. 14, 1953 RADIO DIRECTION FINDER Joseph B. Heffner, Jr., Upper Darby, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application February 28, 1951, Serial No. 213,210

Claims. l

This invention relates to radio direction finders, and more particularly is an improvement in indicator systems used with radio direction finders.

In radio direction nding systems for determining the azimuth of a signal wherein a cathode ray tube indicator is used, the cathode ray tube is required to represent the direction from which a signal is received as well as the signal amplitude. In this manner the azimuth of the signal is readily seen as the direction from which the greatest signal amplitude is received. In one of these types of radio direction finding systems, an antenna having a directional receiving pattern is rotated and the amplitude of the signals received are used to determine the amplitude of the diameter of a circle made by rotating the electron beam of a cathode ray tube.

In order to identify the direction of the single antenna with the representation shown on the cathode ray tube screen, several different approaches have been taken. One of these is to have a revolving yoke coil around the neck of the cathode ray tube which serves to magnetically rotate the electron beam in the tube. The yoke is driven in synchronism with the antenna and therefore the beam position is representative of the antenna position. Another system, shown in Patent No. 2,468,110 to Richardson is to apply quadrature voltages, from an oscillator which is oscillating at a high frequency, to the deflection plates of a cathode ray tube to rotate the electron beam. The amplitude of the oscillator output is determined by the amplitude of the signal voltages received. A mask with a radial slot is mounted to be rotatable at the screen of the cathode ray tube. The mask is driven in synchronism with the rotating antenna and the representation shown is a succession of dots.

In both the rotating yoke and rotating mask systems problems of mechanical alignment are presented and expensive motor equipment of the selsyn type is required. These schemes have been favored, however, in view of the diiculty of passing low frequency positional signals, from means such as a goniometer at the antenna, through balanced modulators, transformers and the like to properly position the electron beam in relation to the antenna.

It is an object of the present invention to provide an improved al1-electronic cathode ray tube indicator system for radio direction finders which does not use a motor driven mechanism at the cathode ray tube.

It is another object of the present invention to provide a novel and inexpensive all-electronic cathode ray tube indicator system for radio direction finders. w

It is still a further object of the present invention to provide an all-electronic cathode rayY tube indicator system having an improved direction indicating presentation.

These and further objects of the present invention are achieved by providing a cathode:v

ray tube indicator system wherein an oscillator generates oscillations at a frequency which is much higher than the frequency of rotation oi.

a rotatable antenna Whose azimuthal position is sought to be indicated. Signals received by' the antenna are used to control the gain of a variable gain amplifier. rlhe oscillator output is applied to the variable gain amplifier. The amplifier output is then split into four phases and used to rotate the cathode ray beam at a high frequency in a circular path Whose diameter is determined by the amplitude of the received signal. The cathode ray beam is maintained biased oi. Another portion of the oscillator output is split into four phases and used to excite4 a four-phase phase-shifting condenser. This condenser is driven in synchronism with the rotatable antenna and provides an output the phase of the occurrence of which is dependent on the azimuthal position of the antenna. This output is then shaped into a pulse, sharpenedi and then applied to bias on the cathode ray beam for the duration of the sharpened pulse.l The cathode ray tube screen therefore displays a dot pattern indicative of the relative signal.-

amplitude and its azimuth.

The novel features of the invention as as the invention itself, both as to its organization and method of operation, will best be under.- stood from the following description, when read in connection with the accompanying drawing, in which a partial schematic, partial circuit diagram of an embodiment of the invention is shown.

A search antenna, having a directional pat.

vided into two portions. One portion is appliedl vWell as input to the variable gain amplier I8. The variable gain amplifier output is applied to another amplication stage 22. The output from the latter amplification stage 22 is applied, through a coupling transformer 2s, to a phase splitting bridge 2B. This bridge, in a manner well-known in the art, provides a four-phase output which is-applied to the horizontalA di) and vertical 42 deecting plates of a cathode ray tube 28.

The cathode ray tube 28 besides the vertical and horizontal deecting plates has the usual beam-producing means including an electron gun 3B having a cathode 32 and-a` grid3^which-has a bias applied from a bias sourceSt so that fthe electron beam is normally biased oi. The electron beam is directed towardgthe screen` 38 of the cathode ray tube. The tube has the usual power supply provided therefor. Thisiswell known in the art and is-lnot shown here in the interests of maintaining clarity inthedrawing.

l Another portion lof 'the oscillator output .is coupled through a coupling transformer 44 toa second phase .splittingbridge ct. The output of thefbridge `is used to excite-a four-phase phaseshifting Acondenser '33. AThe-*condenser has the.

shaft 50 of its rotor' coupled l-to bedriv'en-in synchronism with the antenna I ofso that the phase of 'its output is always an indication of the azimuth angle made by .the .antenna with a given zero angle position. Y'Ihelfour-'phase phase-shifting condenser 48 fiszfound described inchapter 9 of volume 17 ofthe RadiationLaboratory series. The ibook is by Blackburn, isv entitled Components Handbook and is. published'by the Mc- Graw-Hill PublishingCompany. The condenser 48 'consists of a solid circular plate opposed by a circular plate-divided into four separately insulated quadrants. A rotor plate revolves between these two plates. The four-phase output from the phase-splitting bridge is connected to each ofthe quadrants of the-divided circular plate. Y Output is derived-fromthefsolid circular plate. The output is a voltage/,whose occurrence in time is dependent upon the yquadrant of thev condenser plate wherein the rotor is positioned and thisof coursedepends upon the antenna position.k

The condenseroutput is applied Yto a series of pulse shaping ampliers 52, 5d and the outputV of thesepulse shapers is differentiated by a dinerentiating-network 56. The differentiating network output is appliedto the g-rid'i of the cathode ray tube 28 to overcome the blanking bias and to permit the electron beam to reach the screen for the duration of thev differentiated pulses. In vewof the synchronism ofthe condenser rotor with the antenna, the cathode ray tube screen 38 will show a bright dot whose angular position from a given zero position corresponds to the azimuth angle of the antenna. In view-of the variable gain'amplier connections, the distance of the dot from the center of the cathode ray tube-screen correspondsto the amplitude of the signal received. Therefore, upon the antenna being rotated, a typical pattern 58 is shown on the cathode ray tubescreen 38. The azimuth of the signal is readily identified as the ang-1e at which the dots on the screen-are farthest from the center ofthe tube. Eifectively, a polar coordinate plot of Ithe signals received by Athe rotatingantenna is made on the cathode ray tube screen.

.By wayof example, a typical frequency used for the oscillator iskc. ,for a rotation speed for the antenna of 35 cycles per minute using a. 5-inch cathode ray tube. In general, the greatest pattern detail will be obtained by using a small duty cycle, a high oscillator frequency and a low rotational speed for the antenna. The duty cycle is dependent on the tube diameter, the spot diameter and the amount of elliptical distortion that can be tolerated. For a given tube diameter. the greater the difference'betweentheantenna rotation speed and the oscillation frequency, the

`faster the rise time that can be plotted without the dots becoming discontinuous. This system permits `the entire screen and signal pattern to be seen .simultaneously when long persistence phosphorsare-used-in the cathode ray tube even at slow antenna scan rates.

VYFrom .the foregoing description, it will be readily apparent that there has been provided -anli`mproved, novel, inexpensive, al1-electronic cathode ray tube indicator system for radio direction nnders.- Although there has been shown and described .but a single embodiment of Vthe present invention, .it lshould -be readily apparentthat many changes may be madeinthe particular embodiment herein disclosedand thatmanyvother embodiments are possible, all within the spirit and scope ofthe present invention. Y Itis therefore `desired thatY the foregoing shall be-taken as illustrative andnotas limiting.

What is claimed is: 1.V An electronic polar coordinate 4indicator system-fora rotating antenna comprisinga cathodeY ray tube having ascreen, meansin said tube 4for producing an electron beam directed -rtoward saidv screen,lmeans for rotating said beamata speed.

rotating said antenna, a cathode ray 'tube having a screen, means in said tube for producing an electron beam directed toward saidscreen,

means to generate electrical voscillations .at a.

frequency which is high when-compared lto the speed of rotation of said antenna, meansto vary the amplitude of said oscillations with-the variations in amplitude of signals received by,v said antenna, means to rotate said electron beam with said amplitude varied oscillations, 'means to maintain said beambias'ed 01T, and means responsive to said rotatable antenna position to bias on said beam only when said beam reaches an angular position while vbeing rotated corresponding to the angular position ofsaid rotatable antenna.

3. A signal azimuth indicating system comprising an antenna having a directional radiation pattern forreceiving said-signals, means to rotate said antenna, a cathode ray tube havinga screen, means in said tube for producing an electron beam directed towardsaidscreen, means rfor* rotating said beam at a speed `which is high compared to the speed of rotation of saidfantenna, means to varyA the diameter` of rotation of said beam responsive to the amplitude of signals received by said antenna, means to maintain .said beam biased off, Vmeans to generate pulses the phase of occurrence of which is determined by the angular position of said antenna, and means to apply said pulses to said cathode ray tube to bias on said beam for the duration of said pulses whereby a dot pattern of the signal field in which said antenna rotates is displayed on said screen.

4. A signal azimuth indicating system comprising a directional antenna for receiving said signals, means to rotate said antenna, a cathode ray tube having a screen, means in said tube for producing an electron beam directed toward said screen, means to generate electrical oscillations at a frequency which is high when compared to the maximum speed of rotation of said antenna, a variable gain amplier to the input of which said oscillations are applied, means to control said amplier gain in accordance With the amplitude of signals received by said antenna, means to rotate said electron beam With the output from said variable gain amplifier, means to maintain said electron beam biased off, means to generate pulses the phase of the occurrence of which is determined by the angular position of said antenna, means to differentiate said pulses, and means to apply said diierentiated pulses to said cathode ray tube to bias on said 6 beam whereby a dot pattern of the signal field in which said antenna rotates is provided on said cathode ray tube screen.

5. A signal azimuth indicating system as is recited in claim 4, wherein said means to generate pulses the phase of the occurrence of Which is determined by the angular position of said antenna comprises a four-phase phase-shifting condenser having its rotor rotated in synchronism with said directional antenna. means to split a portion of said generated oscillations into four separate phases, means to excite said four-phase phase-shifting condenser with the output of said last-named means, and pulse shaping means to Which the Variable phase output of said fourphase phase-shifting condenser is applied.

JOSEPH B. HEFFNER, JR.

References Cited in the lle of this patent UNITED STATES PATENTS Number Name Date 2,403,967 Busignies July 16, 1946 2,407,281 Johnson et al Sept. 10, 1946 2,475,612 Hansel July 12, 1949 

